RFID tags are known in the art. These so-called tags often assume the form factor of a label or a literal “tag” but are also sometimes integrated with a host article and/or its packaging. RFID tags typically comprise an integrated circuit and one or more antennas. The integrated circuit typically carries out a variety of functions including modulating and demodulating radio frequency signals, data storage, and data processing. Some integrated circuits are active or self-powered (in whole or in part) while others are passive, being completely dependent upon an external power source (such as an RFID tag reader) to support their occasional functionality.
There are proposals to utilize RFID tags to individually identify individual items. The Electronic Product Code (EPC) as managed by EPCGlobal, Inc. represents one such effort in these regards. EPC-based RFID tags each have a unique serial number to thereby uniquely identify each tag and, by association, each item associated on a one-for-one basis with such tags. (The corresponding document entitled EPC Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960 MHz Version 1.0.9 is hereby fully incorporated herein by this reference.)
Being able to read and then uniquely identify each item within a manufacturing facility, a cargo container, a staging area, or in a retail display area offers any number of useful opportunities. Unfortunately, the very nature of RFID-based technology, coupled with a correspondingly potentially enormous number of individually-tagged items also gives rise to a number of challenges as well. As one example in these regards, reading RFID tags is often not a particularly speedy transaction. As a result it can take a significant amount of time to read a large number of RFID tags in some application settings.
At the same time, many applications settings can contain a large number of RFID tags to be read (such as thousands, tens of thousands, or even hundreds of thousands of tags). In addition, and exacerbating the relevant challenges, is that many such application settings presently frequently (and unpredictably) dynamic circumstances. For example, previously-read RFID tags can be moved within the application setting or can leave the application setting. Similarly, new un-read RFID tags can enter the application setting (in small or large quantities).
If, for example, 10,000 RFID tags all simultaneously receive a query command they will all at least attempt to participate in that inventory cycle. As a result, this inventory cycle could take several seconds to complete. If another RFID tag enters this inventory zone during this time, that new RFID tag will typically have to wait for a next query command. That new RFID tag, however may be in this particular area less than the several seconds it might have to wait before the reader is ready to start that next inventory cycle. In such a case the reader will be unaware of the transitory presence of that new RFID tag. The number of tags that could potentially be missed is large enough in some application settings to render this solution impractical.
Furthermore, in a large area such as the sales floor of a large retail store many RFID tags may only have power for brief moments of time as they move from time to time within that area. In that case many such RFID tags may well miss the beginning of many such inventory cycles and consequently never be seen as they move out of the area being inventoried before a new such cycle begins.
In an attempt to redress such circumstances to at least some extent, the aforementioned Electronic Product Code (EPC) as managed by EPCGlobal provides for a number of different RFID tag interrogation modes. The best mode for such circumstances might be the worst mode for other circumstances. This, in turn, permits a given enterprise to select, for on-going uninterrupted use, a particular interrogation mode that best suits the relative volume and dynamic circumstances as tend to characterize their application setting. While such an approach has been helpful, however, there nevertheless remain unmet needs in these regards.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.